Do replacing the o2 sensors make that much of a difference? I know I had one of the 02 sensors on The Beast replaced because it was bad and throwing a code, but I left the other one alone. That was right after I got the truck. So one of the sensors is almost 4 years old and has ~40,000 miles on it, and the other is probably 10 years old with 152,000 miles. The truck just passed emissions a couple of months ago. I haven't given it much thought because I really haven't noticed anyone saying they were replacing an o2 sensor for FE unless they were talking about upgrading to a heated o2 sensor.

Hey how did I miss this thread for so long . . . been working like crazy lately. Improbcat nice work on the rear belly pan - I was really concerned about the air flow in or out of the rear fenders - them being so open to the big space where a trunk should have been under the rear . . . could put a full spare tire in that space or a bigger gas tank! Be interested in how you make out with the FE after that covering.

I did 48mpg to home today and 55mpg coming back - this after my run out to Cape Cod on Tuesday this past week where I got 44mpg going out at highway speed (about 1-2mpg more than usual) and 49.0mpg coming back on a slower Route 6 with a lot of stops. It seems that the Racing Disks help FE at lower speed (40mph) a lot more than at higher speeds (65mph) probably because the air flows right over them at higher speeds.

I think you have inspired me to add the Foam Board center rear belly pan on mine next chance I get into the garage so I can see if it affects FE.

JanGeo what are you doing to get those numbers from your xB? I am lucky to get 33mpg out of mine....

When you install the iridiums how are you going to gap them?

- Alan

Hey Alan

You xB guys should be a member of ScionLife.com - plenty of good info there on all sorts of things. The gap on the Irridium plugs for best performance (FE) is pretty big 0.044" if you get the EIX-11 they are already gapped bigger than the standard small gap of 0.032". Of course I got the standard ones so I will have to pry them open - maybe installing them later this week . . . finally!

Most of my high mileage is typical hypermiling technique but some of it is the Synlube that I added after gentle engine break in at 3700 miles (now at 22080) which provides better lubrication and no oil changes . . . plus 40-42psi in the tires and 3-4 oz of acetone in the gas every 10 gallons. The Racing Disks seem to help a little too.

Get a Scangauge and back off the gas sooner and you too can get great mileage but I think a lot of it is the lube in the engine, power steering and tranny running the Synlube. I get high 30's going up hills on the highway and typically cruize at 65mph in the low to mid 40 mpg.

My box has over 105K on it, and still has the original O2 sensors. The one front of the cat is my primary concern as the replacement interval is 100K or less and while I haven't been throwing codes, the engine is not running as well as it could. I've also been getting some carbon on my plugs, which indicates it is running a bit rich, and since the O2 sensor is a vital part of that I figure replacing it is a good way to start.
If your car is running well don't worry about the O2 sensors, but since mine isn't I'm looking for likely causes.

Its running fine, but I still think I should be getting somewhat better mileage than I actually am. I checked and it appears I can replace all the o2 sensors on the truck for under $100. I've also been thinking about plug wires. I can't remember if those were replaced when I bought the truck or not. I know the cap & rotor were replaced, and I saw that someone had put some cheap copper plugs in it so I replaced the plugs with some OEM Platinums. Later on this week I'm coming up on some time off, I may just replace the o2 sensors and rig up my HAI.